How the calculation works
The calculator first estimates saturation vapor pressure from the air temperature. It then uses relative humidity to estimate actual vapor pressure and converts that value into grams of water vapor per cubic meter of air.
The saturation-vapor-pressure equation uses the World Meteorological Organization coefficients published in its humidity measurement guidance. The final conversion follows the same near-surface relationship used by the FeelsLike weather service.
The same percentage can produce a different result
At 20°C and 50% relative humidity, the estimate is about 8.6 g/m³. At 30°C and the same 50%, it is about 15.1 g/m³. The percentage stayed the same, but the warmer air contains more water vapor.
That is why relative humidity alone can be awkward when you compare two hours or two destinations with different temperatures. Read why FeelsLike shows absolute humidity for the measurement’s definition and scientific limits.
Use the result for comparison, not as a comfort verdict
Absolute humidity gives you a concrete moisture amount. It does not tell you by itself whether the air will feel pleasant, sticky or dry. Temperature, wind, direct sun, activity, clothing and personal sensitivity can change the experience.
FeelsLike places absolute humidity beside feels-like temperature, wind and rain across the next 24 hours. The web tool can also compare the same measurements with a destination, so you do not need to calculate every hour by hand.
Where this estimate has limits
NOAA’s atmospheric moisture calculator notes that its approximations are intended for natural climate near sea level. Pressure, phase changes below freezing and measurement accuracy can matter in scientific or high-altitude work.
Use an official local forecast for warnings and safety decisions. This calculator is an educational planning tool, not a medical, heat-risk or air-quality instrument.
Sources
- NOAA Air Resources Laboratory: Moisture Calculator
- World Meteorological Organization: Guide to Meteorological Instruments and Methods of Observation
- National Weather Service: Discussion on Humidity
Weather definitions and alert practices can vary by provider and country. Check your local weather authority for warnings and safety decisions.